London: London marked the two-year countdown to the 2012 Olympic Games on Tuesday by throwing open venues to star athletes, issuing a call for 78,000 volunteers and opening the first official Olympic store for sale of mascots and other souvenirs.

A series of activities took place across the city to celebrate the buildup to the opening ceremony on July 27, 2012.

Tuesday`s spotlight was on the Olympic Park site in east London, where athletes were testing out some of the key facilities that are still under construction. The external structures of the main venues are already complete and the arenas are set to be completely finished next year.

Michael Johnson, a former Olympic 200- and 400-meter champion from the United States, will race against youngsters on a specially laid track in the 80,000-capacity main stadium.

British cyclist Chris Hoy, a four-time gold medalist, was the first to try out the velodrome and London mayor Boris Johnson also rode a few laps around the temporary indoor track.

"We are on time and on budget," Johnson said. "What we need now are the people to help put on the greatest show on earth."

Organizers launched a program to recruit 70,000 volunteers and urged people to apply for specialist positions such as doctors, anti-doping personnel and scoreboard operators. The signup for more general volunteer positions will open on Sept. 15.

"Today we enter another new phase of London 2012 — bringing the Great British public onboard," Sports and Olympics Minister Hugh Robertson said. "Volunteers are the heartbeat of every Olympic and Paralympic Games and are crucial to their success. We need skilled and passionate people who have the commitment to make 2012 the best Olympic and Paralympic Games ever."

Johnson announced a separate program to recruit 8,000 "London Ambassadors" who will man key points across the city, such as railway stations and tourist spots, to help guide visitors around the capital.

"These will be the polite, courteous, smiling — without being irritating — faces of the city," Johnson said. "London will be the center of the greatest party on earth."

Organizers urged fans to keep registering their interest in tickets, which will go on sale next year. So far, more than 1.4 million have registered. A total of eight million tickets for the Olympics and two million for the Paralympics will be on sale.

"How will you spend the summer of 2012? Whether it`s buying a ticket, becoming a volunteer, being part of our education or culture programs — there are hundreds of ways you can get involved. Don`t wait. To ensure you don`t miss out, start planning your Games now."

The London 2012 committee opened its flagship merchandising store at St. Pancras International station in central London where, for the first time, soft toys of the child-friendly one-eyed mascots Wenlock and Manderville were available for purchase.

It`s also from St. Pancras where Olympic organizers, athletes and dignitaries took the Javelin bullet train for the six-minute journey to the Stratford International station at the Olympic Park.

From there, the group planned to walk across the new main bridge or "front door" to the Olympic Park and get a firsthand look at progress on the 1-square-mile site. A once-deprived industrial area of the capital is being transformed into a new complex of venues and parkland that will be turned over to the public after the games.

Still to be determined is the future tenant of the Olympic Stadium. West Ham soccer club claimed Monday that it expected to be granted first option to move into the stadium after 2012, but no final decision is expected until later this year.

While the Olympic project is on track and on budget, organizers are under scrutiny as the coalition government carries out 40 billion pounds (USD 61 billion) in public spending cuts to trim the record budget deficit.

The government recently ordered relatively modest cuts of 27 million pounds (USD 41 million) in the budget of the Olympic Delivery Authority, the body responsible for building the venues. The overall construction and infrastructure budget stands at 9.325 billion pounds (USD 14.3 billion).

"We wake up every morning trying to figure out how we can deliver this in a more cost effective and efficient way," Coe said. "We have to recognize that the world has changed. We are in an economic climate where we have to continue to make very strong arguments for why this is a project of national and natural interest."

Coe said organizers have raised more than 600 million pounds (USD 925 million) toward their target of 700 million pounds (USD 1 billion) in domestic sponsorships — a figure that organizing committee chief executive Paul Deighton has called "gravity defying."

"The first thing that goes in any economy is discretionary spending, and yet we`ve punched through," Coe said.